<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <style>
      .annulus {
        position: relative;
        box-sizing: border-box;
        width: 200px;
        height: 200px;
        margin: 50px auto;
        border-radius: 50%;
        border: 16px solid #333;
      }

      .radar-area {
        position: absolute;
        top: -16px;
        left: -16px;
        bottom: -16px;
        right: -16px;
        background-color: transparent;
        border-radius: 50%;
        background-image: conic-gradient(
          #32c5a9 0%,
          transparent 40%,
          transparent
        );
        animation: rotate 3s ease-in-out infinite;
        transform-origin: 50% 50%;
      }

      /* 填充圆坏内区域 */
      .radar-area::before {
        content: "";
        position: absolute;
        top: 16px;
        left: 16px;
        bottom: 16px;
        right: 16px;
        background: #000;
        border-radius: 50%;
      }
      /* 环形头部小圆 */
      .radar-area::after {
        content: "";
        position: absolute;
        width: 12px;
        height: 12px;
        top: 0;
        left: 50%;
        transform: translate(-50%, 2px);
        border-radius: 50%;
        background: #fff;
        box-shadow: 0 0 4px 2px rgb(108, 199, 241);
      }

      @keyframes rotate {
        100% {
          transform: rotate(-360deg);
        }
      }
    </style>
    <div class="annulus">
      <div class="radar-area"></div>
    </div>
  </body>
</html>
